hi i have a 98 blazer with 95k. when i shift my truck into reverse from park there is a loud "TINK" noise coming from the back under the suv. also when i drive on the express way the truck shakes very bad about 60 mph. i am trying to figure out what u joint is bad but i am not to sure on how to check them some people say to jack up the truck to check them and others say to not jack it up. also is it suppose to be in park or neutral? how many u joints does this truck have? and does bad u joints have anything to do with hard shifting from 1st to 2nd?

Thanks for the advice and help.